Problem: Tiffany is 70 years old and Emily is 20 years old. How many years will it take until Tiffany is only 3 times as old as Emily?
Answer: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Tiffany will be $70 + y$ years old and Emily will be $20 + y$ years old. At that time, Tiffany will be 3 times as old as Emily. Writing this information as an equation, we get: $70 + y = 3 (20 + y)$ Simplifying the right side of this equation, we get: $70 + y = 60 + 3 y$ Solving for $y$ , we get: $2 y = 10$ $y = 5$.